PSI - Issue 60

B.P. Kashyap et al. / Procedia Structural Integrity 60 (2024) 494–509 B.P. Kashyap et al. / Structural Integrity Procedia 00 (2023) 000 – 000 13

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4. Summary and concluding remarks High temperature deformation and damage behavior occur by several mechanisms operating in parallel or sequentially in different parts of the material. There appear to be large variations in the parameters of the constitutive relationships, which could arise from the nature of the material and heterogeneously evolving microstructure during deformation. It would be more useful for understanding the flow properties if these two approaches are integrated appropriately. The analysis of high temperature deformation and damage behavior in the single phase, quasi-single phase, and two phase-materials with concurrent substructure and microstructure evolution, including cavitation, leads to interesting conclusions listed below.  While grain boundary sliding is the dominant deformation process in fine grained materials, it is necessary to provide an accommodation process for the same in order to avoid damage initiation. The common accommodation processes occurring are diffusional and intra-granular deformation, which result in grain size, grain morphology, and texture changes, resulting in hardening, softening, or pseudo-steady state flow behavior.  Grain boundaries and grain interior both play complementary roles in deformation. In type 316L stainless steel, the strength coefficient of the Hollomon relationship decreases with increasing grain size at 973 K. The occurrence of flow hardening is dominated in the beginning by grain boundary resistance to dislocation motion.But, the redistribution of geometrically necessary and statistically stored dislocations in the form of cell structure, on continued deformation to larger strain, make the grain interior as the dominant source of strengthening; with both the effects occurring in a coordinated manner in polycrystalline material.  The lack of accommodation for grain boundary sliding causes stress concentration at grain boundaries or triple points which, in turn, gives rise to cavity formation. The development of cavities is also connected with the mechanisms of deformation. As such, there existsan interrelationship between the nature and governing constitutive relationships for deformation, and that for concurrent microstructure evolution. Interestingly, the flow behavior, cavitation, and grain size are found to be interdependent and concurrently related to each other through the strain rate sensitivity index. References Ammouri, A. H., Kridli, G., Ayoub, G., Hamade, R. F., 2015. Relating Grain Size to the Zener-Hollomon Parameter for Twin-Roll-Cast AZ31B Alloy Refined by Friction Stir Processing. Journal of Materials Processing Technology 222, 301-306. https://doi.org/10.1016/j.jmatprotec.2015.02.037 Ashby, M. F., Verrall, R. A., 1973. Diffusion-Accommodated Flow and Superplasticity. Acta Metallurgica 21, 149-163. https://doi.org/10.1016/0001-6160(73)90057-6 Bakshi, P. K., Kashyap, B. P., 1995. Stress-Strain Rate Relations for High-Temperature Deformation of Two Phase Al-Cu Alloys. Journal of Materials Science 30, 5065-5072. https://doi.org/10.1007/BF00356050 Beere, W., Speight, M. V., 1978. Creep Cavitation by Vacancy Diffusion in Plastically Deforming Solid. Metal Science 12, 172-176. https://doi.org/10.1179/msc.1978.12.4.172 Cao, F., Li, Z., Zhang, N., Ding, H., Yu, F., Zuo, L., 2013. Superplasticity, Flow and Fracture Mechanism in an Al-12.7Si-0.7Mg Alloy. Materials Science and Engineering A 571, 167-183. https://doi.org/10.1016/j.msea.2013.02.010 Chokshi, A. H., 1986. The Development of Cavity Growth Maps for Superplastic Materials. Journal of Materials Science 21, 2073-2082. https://doi.org/10.1007/BF00547949 Chung, D. W., Cahoon, J. R., 1979. Superplasticity in Aluminium-Silicon Eutectic. Metal Science 13, 635-640. https://doi.org/10.1179/msc.1979.13.11.635